macos: pkgbuild.sh should not be tracked by git

macos: pkgbuild.sh should not be tracked by git

The automatically generated pkgbuild.sh file should not be tracked by
git. To fix this problem, add the name of this file to the proper
.gitignore file.

Reviewed-on: https://gerrit.openafs.org/12343
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 19ffa2b7f09bffea816dda4713ad53f4d8cb93cb)

Change-Id: I581f09deea271dd26e065d35dbf12d6c8480bb8f
Reviewed-on: https://gerrit.openafs.org/12351
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>